1. Field of Invention
The present invention relates to an electricity supply system, in particular to a lithium battery having a simplified separator and electrode layers and a lowest amount of the interfaces inside the battery.
2. Related Art
In the electronic device industry, portability and wireless design are the major trends. Except the lighter, thinner and smaller designs, the flexibility of the electronics is highly focused as well. Hence, an electricity supply system having smaller volume, lighter weight and higher energy density is imperatively required. However, to prolong the life and to increase the energy density of the electricity supply system, the primary electricity supply system obviously cannot satisfy the demands of the current electronics. And this is the reason why the secondary electricity supply systems such as the lithium battery system, fuel cell system, solar cell system become the main stream for their recharge abilities. The lithium battery system is taken as the example for its highly development.
FIG. 1A illustrates the current cell of the lithium battery system. The main structure is constructed by a separator layer sandwiched by a cathode electrode and an anode electrode. The external electrodes of the whole lithium battery system, which are electrically connected to the peripherals, are welded individually to the tabs located in the current collectors of both cathode and anode electrodes. As shown in FIG. 1A, the lithium battery 1 includes a separator layer 11, a first active material layer 12, a second active material layer 13, a first current collector layer 14, a second current collector layer 15 and a package unit 16. The first active material layer 12 is located above the separator layer 11. The first current collector layer 14 is located above the first active material layer 12. The second active material layer 13 is located under the separator layer 11. The second current collector layer 15 is located under the second active material layer 13. The package unit 16 seals the whole stacking structure mentioned above except the two tabs 141 and 151. Accordingly, as the lithium battery 1 provides the electricity to an electronic device 2 (the circuit broad illustrated in FIG. 1A is only one embodiment and is not a limitation for the electronic device 2), the tabs 141 and 151 are electrically connected to the electricity input terminals 21 and 22 of the electronic device 2 so that the electricity stored in the lithium battery 1 is transferred to the electronic device 2. After that, the electricity is transferred to the element area 23 of the electronic device 2 by the layouts. The element area 23 mentioned here may be the circuit layouts or the surface mounted elements, that is, typically includes the logical circuit, active elements, and passive elements and so on.
However, the electrical and safety performances of the lithium battery 1 are dramatically influenced by the characteristics of both the interface between the separator layer 11 and the first active material layer 12 and the interface between the separator layer 11 and the second active material layer 13. Please refer to FIG. 1A, there have four interfaces of the lithium battery 1, i.e. the interfaces between the separator layer 11 and the first active material layer 12, between the separator layer 11 and the second active material layer 13, between the first current collector layer 14 and the first active material layer 12, and between the second current collector layer 15 and the second active material layer 13. For the current lithium battery system, the characteristics of these interfaces are controlled either by solid stacking method or by high-tension winding method (jelly roll) to ensure the good electrical and safety performances of the lithium battery system. Unfortunately, the lithium battery systems made by solid stacking or high-tension winding method are definitely lack of flexibility and even are impossible to be flexed. If the stacked battery or the winded battery is forced to be flexed it would cause the serious damage to the interfaces between the separator layer 11 and the first active material layer 12 and the separator layer 11 and the second active material layer 13.
Moreover, the active anode material may expand or shrink its volume on charge or discharge to exhibit mechanical stress to both sides of the active anode material. Please refer to FIG. 1A, for example, if the second active material layer 13 is the active anode material, the second active material layer 13 is disposed between the separator 11 and the second current collector layer 15. Therefore, the second active material layer 13 exhibits mechanical stress to the separator 11 and the second current collector layer 15 on charge or discharge. After a certain period of time, it is difficult to maintain the same quality of interfaces due to suffer of the repeating volume expansion and shrinkage.
Also, the tab 141 is usually made of aluminum. Because the aluminum can not be soldered directly, the tab 141 have to be connected with a nickel sheet by ultrasonic.
Furthermore, the tabs 141, 151 have to extend outside of the package unit 16. The thickness of the tabs 141, 151 is 100 to 150 um (micro meter), and the thickness of the package unit 16 including the glues is 60 to 120 um. Therefore, there may have a gap between the tabs 141, 151 and the package unit 16 to make the moisture resistance and the liquid barrier weaker, which may cause the outside moisture to permeate inside, or the inside electrolyte to leak out and damage the circuit.
Please refer to FIG. 1B, the stack type battery is provided with a plurality of unit cells (the lithium battery 1) stacked in a stack direction. Due to each lithium battery 1 has four interfaces as above mentioned, the total number of the interfaces would be increased accordingly. Along with the active anode material may expand or shrink on charge or discharge to exhibit mechanical stress, the reliability of the stack type battery may be influenced when one of the interfaces does not contact well. Also, the amount of the interfaces would influence the fluidity and permeability of the electrolyte. When the amount of the interfaces is increased, it costs more time to make the electrolyte permeate uniformly. Moreover, the electrolyte distribution may be not uniform even after long time that will decrease the efficiency of the battery.
Also, the leads of each battery 1 have to be connected in parallel before the tabs 141 and 151 are electrically connected to the electricity input terminals 21 and 22 of the electronic device 2. When the number of the leads is increased, the reliability and the yield rate of the welding are decreased.